1. Field of the Invention
The present invention relates to a high-strength caulking technique capable of firmly fixing a hollow or solid columnar body to a metal plate body. Particularly, the present invention relates to a high-strength caulking technique capable of firmly fixing a hollow or solid columnar body to a plate body made of magnesium or a magnesium alloy. Also, the present invention relates to a caulking technique of a resin molded body made of a thermoplastic resin with a hollow or solid columnar body made of a material having a higher melting point than that of the thermoplastic resin.
2. Description of the Background Art
Caulking of this kind of a plate body with a columnar body has been conventionally performed as follows. In Patent Reference 1, a flange part is formed at the middle part of a shaft body side as shaft caulking, and a circular hole is punched in the side of a plate body which is a press component as a caulked object. The tip part of the shaft body inserted into the circular hole is crushed by a caulking machine for exclusive use. The press component is sandwiched and caulked between the crushed head part of the shaft body and the flange part. Or, a more complicated specific shape is formed at the side of the shaft body, and the columnar body is joined to the plate body by press-fitting the shaft body into the circular hole opened in the press component.
However, a large flange part must be provided at the middle part of the shaft body in order to sandwich the press component between the crushed head part of the shaft body and the flange part. Thereby, it is necessary to cut a shaft material which is about 50% thicker than a shaft diameter required for product use to produce a flange shape, which increases a material cost and a process cost. The manufacture cost is also increased for forming the specific shape, which limits the cost reduction.
On the other hand, in recent years, attentions have been particularly focused on magnesium or a magnesium alloy which has lightweight, easily absorbs vibration and shock, has high electromagnetic wave shielding ability, and has excellent recycling property as case uses for portable phones. However, the worse processability thereof causes extremely difficult caulking of a shaft with, particularly, a thin plate. In Patent Reference 2, the following caulking has been proposed as the caulking of the magnesium or magnesium alloy material. A caulking punch is preheated. While the preheated caulking punch is rotated, the punch is pressed against a top part of a caulking pin as a molded product to performing caulking. This method deforms the shaft to process as in the above Patent Reference 1. This method has had problems such as large-scale devices required for increased manufacture cost and low flexibility of the design because of indispensable shaft deformation.
Conventionally, press fitting or adhesion using a solvent has been mainly performed as a method for fixing a shaft such as a metal or the like to a plate made of, for example, a thermoplastic resin molded body. However, the press fitting could not secure sufficient strength when the thickness of the resin molded plate is reduced. The adhesion method using the solvent could not fundamentally attain the perpendicular degree easily, had inconvenient freedom of the shape, required long junction time to reduce the manufacturing efficiency, and was hardly introduced as a fixing method for precision components.
On the other hand, as a method for ultrasonically melting the resin molded body to press-fit the melted resin, a method using the following device has been proposed (for example, see Patent Reference 3). On a first member made of a thermoplastic resin, a second member having a high melting point was arranged. A processing surface of a processing horn is abutted on a flat surface formed on the second member. While supersonic vibration is applied to the processing horn, pressing force is applied between a receiving tool and the processing surface of the processing horn. The second member is partially press-fitted into the first member melted by supersonic vibration heat to connect and fix the second member to the first member. While a concave portion is formed in at least a part of the processing horn, at least a part of the end part of the flat surface of the second member is located below the concave portion, and the second member is arranged so that the first member melted in press-fitting the second member is turned to the flat surface side of the second member, and covers at least a part of the end part of the flat surface.
However, such a method to press the second member on the first member inevitably causes reduction in the perpendicular degree of the second member. Since the method fixes the first member using the resin turned to the flat surface side of the second member, and the obtained structure requires a sufficient turing amount, firm combination cannot be maintained if the melted resin is blocked in the concave portion of the processing horn, and the management is troublesome. Since the flat surface of the second member is indispensable, second member cannot be applied to the shaft body free from such a flat surface. Furthermore, the first member must have a thickness for embeding the flat surface of the second member, and cannot be applied to the reduction in the thickness of the plate. The processing horn having a specific shape is required for every kind of the second member, and unfortunately, the cost is increased.    [Patent Reference 1]    Japanese Unexamined Patent Publication No. 2003-260529    [Patent Reference 2]    Japanese Unexamined Patent Publication No. 2003-266136    [Patent Reference 3]    Japanese Unexamined Patent Publication No. 59-145112